Current sensing switch

ABSTRACT

A current sensing switch having a pair of magnetically operated contacts located in a cavity of a block of non-conductive material and a magnetic field concentrating member adapted to partially surround a current carrying conductor such that the magnetic flux produced therein is confined to a predetermined path with the flux path being in close proximity to the cavity and the magnetically operated contacts therein. The switch further includes a field compensating magnet for aiding or bucking the magnetic field produced by current flow through the conductor.

United States Patent Kuehn, IH [4 1 Aug. 15, 1972 [54] CURRENT SENSING SWITCH 72 I t An K H Primary Examiner-Roy N. Envall, Jr. nven or drew uehn I St Paul, Minn Atwmey Burd Braddock & Banz [73] Assignee: Systematics, Inc., St. Paul, Minn. 22 Filed: March 8, 1971 [57] ABSTRACT Appl. No.: 121,984

US. Cl ..335/204, 335/153 Int. Cl. ..H0lh 53/10, HOlh 51/28 Field of Search ..335/204, 205, 207, 153

References Cited UNITED STATES PATENTS Wahlgren ..335/204 Shoffa ..335/204 A current sensing switch having a pair of magnetically operated contacts located in a cavity of a block of non-conductive material and a magnetic field concentrating member adapted to partially surround a current carrying conductor such that the magnetic flux produced therein is confined to a predetermined path with the flux path being in close proximity to the cavity and the magnetically operated contacts therein. The switch further includes a field compensating magnet for aiding or bucking the magnetic field produced by current flow through the conductor.

4 Claims, 5 Drawing Figures PATENTEDAUG 15 I972 INVENTOR ANDREW KUEH/V in BY 1, 54M 1 5 ATTORNEY CURRENT SENSING SWITCH BACKGROUND OF THE INVENTION In my copending application Ser. No. 854,631, filed Sept. 2, 1969 and entitled ENGINE STARTER AND TEMPERATURE CONTROL SYSTEM, an electrical circuit is disclosed and claimed for automatically starting an internal combustion engine when its temperature falls below a certain predetermined value and for shutting down the engine when the temperature rises to a second predetermined elevated value. This control circuit includes apparatus for detecting when the engine has started and is self-running so that the starter motor can be cut off to prevent damage thereto. This is accomplished by sensing the current flowing from the battery, through the starter motor cable to the motor itself. When the starter motor is first energized, it draws a substantial current because of the high starting torque requirements. After the engine has started and is selfrunning, the current flowing to the starter motor drops off to a relatively low value. This variation in starter motor current requirements is sensed and used to control the energization of the starter motor.

The above mentioned pending application discloses the use of a magnetic reed type switch which is inductively coupled to the cable leading from the engine bat tery to the starter motor. When the starter is first energized, the heavy current flow causes the contacts of the reed switch to close thereby completing a holding cir cuit through a relay. When the engine is free-running, thus lowering the torque requirements of the starter motor, the current flowing from the battery to the starter motor drops below a predetermined value and the contacts of the reed switch open, breaking the circuit to the holding relay and disconnecting the starter motor from the battery.

The present invention pertains to a preferred embodiment of a current sensing switch suitable for use in the engine starting control circuit of the aforereferenced pending application. Of course, a switch of the type described and claimed herein may find use in many applications and limitation to use in an engine starting control circuit is not intended and should not be inferred.

The preferred embodiment comprses a block of nonconductive, non-magnetic material having a cavity formed therein. This cavity is adapted to contain a socalled magnetic, glass-enclosed reed switch, many forms of which are commercially available. The reed switch utilized includes, for example, a pair of normally open conductive contacts formed at least in part from a high permeability material such that when subjected to a magnetic field of a predetermined magnitude, the contacts will be attracted to each other and will close. Mounted on the block is a tubular member also formed from a low reluctance material such as soft iron. This tubular member is adapted to partially surround a current carrying conductor and is shaped so as to concentrate magnetic lines of flux produced thereby to a prescribed path. This path is in close proximity to the cavity formed in the block so that the magnetic field will be concentrated in the location occupied by the reed type switch.

Further, the preferred embodiment of the invention incorporates a field compensating magnet which can be made to aid or buck the field produced in the prescribed path by current flow through the conductor so that a measure of control over the opening and closing of the reed switch contacts can be achieved.

Accordingly, it is a primary objective of this invention to provide a novel current sensing switch which is simple in construction, inexpensive to manufacture, but which provides reliable operation over many cycles of use.

The foregoing and other more detailed and specific objectives will become apparent from a consideration of the following detailed description of the preferred embodiment when viewed in light of the drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of the preferred embodiment of the current sensing switch;

FIG. 2 is a side view;

FIG. 3 is an end view;

FIG. 4 is a bottom view; an

FIG Sis a view taken along line 55 in FIG 2.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. I, there is illustrated a perspective view of the current sensing switch of this invention. As is illustrated, the switch comprises a block 10 of a non-magnetic material such as plastic, ceramic, aluminum or the like. As can best be seen in FIG. 5, the block 10 has formed therein a cavity or recess 12 in which is located a glass envelope 14 containing and enclosing a pair of electrical switch contacts 16. The contacts 16 are formed from a high permeability magnetic material such that when exposed to a magnetic field of a predetermined force, the contacts are attracted together to complete a circuit between tenninals l8 and 20. Such reed type switches are well known in the art and are commercially available.

The envelope 14 is retained in the cavity 12 by means of a cover plate 22 (FIG. I) which is secured to the block 10 by means of the screw fastener 24. The cover plate 22 is formed from a non-magnetic material such as aluminum or plastic.

Also mounted on the top surface of block 10 is a magnetic field concentrating means indicated generally by numeral 26 which in the preferred embodiment comprises a generally U-shaped channel 28 having horizontally extending notches 30 and 32 on either side thereof. Secured to the inside surface of the leg portions of the U-shaped channel are L-shaped angles 34 and 36. More specifically, screws 38 pass through channel 28 and enter a tapped hole in the angles 34 and 36. The channel 28 and the angles 34 and 36 are formed from a material such a soft iron and possess a relatively high magnetic permeability and low reluctance.

As best be seen in FIGS 1 and 5, block 10 has a step 40 of a height approximately equal to the thickness dimension of the angle 36. Hence, when the angle 36 passes between the block 10 and the cover plate 22, the cover plate will lie flat against the block 10 and angle 36. Angle 34 on the other hand rests on top of the cover plate 22.

The length of the notches 30 and 32 cut in the channel 28 exceeds one-half the length of the channel and the length of the angles 34 and 36 are approximately the same as the length of the channel leg remaining after the notches 30 and 32 are formed. Hence, the angles 34 and 35 do not abut one another, but instead a gap or slot of predetermined width exists between the opposed edges of the horizontal portion of the angles 34 and 36. This slot is positioned immediately above the mating portions of the contacts 16 of the reed switch.

While the field confining means 26 is illustrated as including the notched U-shaped channel 28 and the angles 34 and 26, it could just as well be formed from a single tubular piece having notches 30 and 32 in opposed sides and a slot cut in the bottom surface which communicates with the slots to define the gap.

The screw 24 passes through a bore 42 drilled through the block 10. The bore 42 is adapted to con tain a permanent magnet 44 in the form of a cylinder and having an axial aperture therethrough to accommodate the screw 24. Screw 24 also serves to hold a rotatable arm 46 (FIG 4) on the bottom surface of block 10. Arm 46 is formed from a magnetic material and is used to direct or steer the magnetic lines of force from the permanent magnet 44 in which it is in contact to a desired location on the assembly. In lieu of permanent magnet 44, a high permeability material may be substituted and utilized for the purpose of controllably guiding the magnetic flux path.

In use, the current sensing switch is slipped over current carrying conductor by passing the conductor through the U-shaped channel 28. Current flowing through the conductor causes a magnetic field to be established in the field concentrating device 26 and because of the notches 30 and 32 formed therein, the magnetic lines of force are directed across the gap or slot formed between the horizontal segments of angles 34 and 36. Since this gap is located immediately above the contacts of the reed switch, the path of lowest reluctance across the gap is through the magnetic material of the contacts themselves. Hence, if the field in proximity of the slot is sufficiently high, the contact 16 will close.

The field produced by the permanent magnet 44 can be made to aid or oppose the field produced by current flowing through the conductor encompassed by channel 28 in the neighborhood of the slot or gap. Selective positioning of arm 46 provides a degree of control over the magnitude of the field effectively applied to the contacts of the reed switch, the field being produced by the current flow through the conductor which, in turn, determines the amount of current flow at which contact closure will occur.

While I have shown and described a preferred form of the invention, it should be apparent that one skilled in the art may modify the arrangement in certain respects and that therefore the scope of the invention is to be determined from the following claims. 8

Iclaim:

l. A current sensing switch adapted to inductively couple a current carrying conductor for sensing when the current therethrough exceeds a predetermined threshold, comprising:

a. a block of non-magnetic material having a cavity formed therein;

b. a pair of normally open contacts enclosed in a non-conductive envelope, arranged to close when subjected to a magnetic field above a predetermined threshold; 0. means securing said non-conductive envelopes in said cavity;

d. magnetic field concentrating means adapted to at least partially surround a current carrying conductor attached to said block, for confining the magnetic flux flowing therethrough to a predetermined path a portion of which is in close proximity to said cavity; and

e. magnetic field compensating means for producing a magnetic flux adjustable from to opposing the magnetic flux in said concentrating means resulting when current flows through said conductor.

2. Apparatus as in claim 1 wherein said magnetic field concentrating means comprises a tubular member formed from a high permeability material having longitudinal notches on opposing sides thereof and a transverse slot formed in the tubular portion between said notches and communicating with said notches.

3. Apparatus a in 2 1 wherein said tubular member fastened to said block such that said transverse slot is located immediately adjacent to said cavity' 4. Apparatus as in claim 3 wherein said magnetic field compensating means comprises a permanent magnet contained within said block and an amt formed of high permeability material abutting said permanent magnet and positionable with respect to said slot.

my UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTEN Patent No. 3 ,684 ,988 Dated August 15 1972 Inventor) Andrew Kuehn III It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as. shown below:

I" a "i Column 3, line 2, "35" should be 36 Column 3, line 10, "26" should be --36-.

Column 4, line 30, after "from" -aidingis omitted.

Column 4, line 39, "Apparatus a in 2 1" should be Apparatus as in Claim 2---.

Signed and sealed this 9th day of January 1973.

:SEAL) \ttest:

EDWARD M.PLETCHER,JR. ROBERT GOTTSCHALK \ttesting Officer Commissioner of Patents 3 UNITED STATES PATENT oFmcE CERTEFICATE 0F CGEC'HN Patent No. 3,684,988 Dated Agust 15, 1972 In entor( Andrew Kuehn It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 2, "35" should be 36.

Column 3, line 10, "26" should be -36-.

Column 4, line 30, after "from" aiding is omitted.

Column 4, line 39, "Apparatus a in 2 1" should be Apparatus as in Claim 2.

Signed and sealed this 9th day of January 1973- BEAL) :test

)WARD M.PLETCHER,JR. ROBERT GOTTSCHALK :testing Officer Commissioner of Patents 

1. A current sensing switch adapted to inductively couple a current carrying conductor for sensing when the current therethrough exceeds a predetermined threshold, comprising: a. a block of non-magnetic material having a cavity formed therein; b. a pair of normally open contacts enclosed in a non-conductive envelope, arranged to close when subjected to a magnetic field above a predetermined threshold; c. means securing said non-conductive envelopes in said cavity; d. magnetic field concentrating means adapted to at least partially surround a current carrying conductor attached to said block, for confining the magnetic flux flowing therethrough to a predetermined path a portion of which is in close proximity to said cavity; and e. magnetic field compensating means for producing a magnetic flux adjustable from to opposing the magnetic flux in said concentrating means resulting when current flows through said conductor.
 2. Apparatus as in claim 1 wherein said magnetic field concentrating means comprises a tubular member formed from a high permeability material having longitudinal notches on opposing sides thereof and a transverse slot formed in the tubular portion between said notches and communicating with said notches.
 3. Apparatus a in 2 1 wherein said tubular member fastened to said block such that said transverse slot is located immediately adjacent to said cavity.
 4. Apparatus as in claim 3 wherein said magnetic field compensating means comprises a permanent magnet contained within said block and an arm formed of high permeability material abutting said permanent magnet and positionable with respect to said slot. 